Adaptec 29320LPE User Guide - Page 16

What is SCSI?, SCSI IDs, Terminating the SCSI Bus, Card, the Boot SCSI ID setting in the SCSI

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Chapter 4: Understanding SCSI ● 16 What is SCSI? SCSI (pronounced "scuzzy") stands for Small Computer Systems Interface. SCSI is an industry standard computer interface for connecting SCSI devices (such as a disk drive, CD-ROM drive, or scanner) to a common SCSI bus. A SCSI bus is an electrical pathway that consists of a SCSI card installed in a system and one or more SCSI devices. SCSI cables are used to connect the devices to the SCSI card. For the SCSI bus to function properly, a unique SCSI ID must be assigned to the SCSI card and each SCSI device connected to it, and the SCSI bus must be properly terminated. SCSI IDs Each device attached to an Adaptec SCSI Card, as well as the Adaptec SCSI Card itself, must be assigned a unique SCSI ID number from 0 to 15 for each of the two SCSI buses. A SCSI ID uniquely identifies each SCSI device on the SCSI bus and determines priority when two or more devices are trying to use the SCSI bus at the same time. Refer to the device's documentation to set the SCSI ID. Here are some general guidelines for SCSI IDs: ● For internal SCSI devices, the SCSI ID is set by configuring a jumper on the device. ● For external SCSI devices, the SCSI ID is set with a switch on the back of the device. ● SCSI ID numbers do not need to be sequential, as long as the Adaptec SCSI Card and each device has a different number. For example, on each of the two SCSI buses you can have an internal SCSI device with ID 0, and an external SCSI device with ID 6. ● SCSI ID 7 has the highest priority on the SCSI bus. The priority of the remaining IDs are in descending order: 6 to 0, then 15 to 8. ● The Adaptec SCSI Card is preset to SCSI ID 7 and should not be changed. This gives the card the highest priority on the SCSI bus. ● Most internal SCSI disk drives come from the factory preset to SCSI ID 0. ● If you have 8-bit (or Narrow) SCSI devices, they must use SCSI IDs 0, 1, 2, 3, 4, 5, or 6. SCSI ID 0 is recommended for the first SCSI disk drive. ● If you are booting your system from a SCSI disk drive connected to the Adaptec SCSI Card, the Boot SCSI ID setting in the SCSISelect utility must correspond to the SCSI ID of the device from which you are booting. By default, the Boot SCSI ID is set to 0. We recommend that you do not change this setting. ● With the SCSISelect disk utility feature, you can confirm/view which SCSI ID is assigned to each device. See Configuring the Adaptec SCSI Card with SCSISelect on page 34. Terminating the SCSI Bus To ensure reliable communication on the SCSI bus, the ends of the SCSI bus must be properly terminated. This is accomplished when the device at the end of each cable, or the end of the cable itself, has a terminator installed (or enabled). Terminators must be removed, or termination must be disabled, on devices between the ends of each cable.

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Chapter 4: Understanding SCSI
●
16
What is SCSI?
SCSI (pronounced “scuzzy”) stands for Small Computer Systems Interface. SCSI is an industry
standard computer interface for connecting SCSI devices (such as a disk drive, CD-ROM drive,
or scanner) to a common SCSI bus.
A SCSI bus is an electrical pathway that consists of a SCSI card installed in a system and one or
more SCSI devices. SCSI cables are used to connect the devices to the SCSI card.
For the SCSI bus to function properly, a unique SCSI ID must be assigned to the SCSI card and
each SCSI device connected to it, and the SCSI bus must be properly terminated.
SCSI IDs
Each device attached to an Adaptec SCSI Card, as well as the Adaptec SCSI Card itself, must be
assigned a unique SCSI ID number from 0 to 15 for each of the two SCSI buses. A SCSI ID
uniquely identifies each SCSI device on the SCSI bus and determines priority when two or
more devices are trying to use the SCSI bus at the same time.
Refer to the device’s documentation to set the SCSI ID. Here are some general guidelines for
SCSI IDs:
●
For internal SCSI devices, the SCSI ID is set by configuring a jumper on the device.
●
For external SCSI devices, the SCSI ID is set with a switch on the back of the device.
●
SCSI ID numbers do not need to be sequential, as long as the Adaptec SCSI Card and each
device has a different number. For example, on each of the two SCSI buses you can have an
internal SCSI device with ID 0, and an external SCSI device with ID 6.
●
SCSI ID 7 has the highest priority on the SCSI bus. The priority of the remaining IDs are in
descending order: 6 to 0, then 15 to 8.
●
The Adaptec SCSI Card is preset to SCSI ID 7 and should not be changed. This gives the
card the highest priority on the SCSI bus.
●
Most internal SCSI disk drives come from the factory preset to SCSI ID 0.
●
If you have 8-bit (or Narrow) SCSI devices, they must use SCSI IDs 0, 1, 2, 3, 4, 5, or 6.
SCSI ID 0 is recommended for the first SCSI disk drive.
●
If you are booting your system from a SCSI disk drive connected to the Adaptec SCSI
Card, the Boot SCSI ID setting in the SCSI
Select
utility must correspond to the SCSI ID of
the device from which you are booting. By default, the Boot SCSI ID is set to 0. We
recommend that you do not change this setting.
●
With the SCSI
Select
disk utility feature, you can confirm/view which SCSI ID is assigned to
each device. See
Configuring the Adaptec SCSI Card with SCSISelect
on page 34
.
Terminating the SCSI Bus
To ensure reliable communication on the SCSI bus, the ends of the SCSI bus must be properly
terminated. This is accomplished when the device at the end of each cable, or the end of the
cable itself, has a terminator installed (or enabled). Terminators must be removed, or
termination must be disabled, on devices between the ends of each cable.